He served as a minor official at the county magistrate's office.
Tips
history
In imperial China, 吏 (lì) referred to minor clerks and functionaries, distinct from 官 (guān), the appointed officials. 官吏 together means the officialdom as a whole.
memory
吏 looks like 史 (history/historian) with an extra stroke — officials were the ones who recorded and enacted history.